The heart muscle receives its blood supply from the coronary artery, which feeds out and around into the outside of the heart muscle. Some time ago it was noticed that reptilian hearts had no arterial supply to the heart muscle. Rather, the reptilian heart blood supply was delivered through the inside wall of the heart directly to the heart muscle. The thought occurred that this could be an alternative to the heart bypass technique which can usually be applied to a patient no more than twice: after two bypass operations the risks outweigh the benefits and the patient is generally without further recourse. In an attempt to imitate the reptilian condition, tiny holes were made in mammalian hearts with hot wires or needles but this met with limited success. Although the holes healed from the outside and did allow for some internal blood delivery, the holes soon healed over entirely and cut off the blood supply. The protocol was then developed using a laser to make the holes and this met with much greater success. This technique is known as transmyocardial revascularization (TMR).
However, the laser technique introduced a host of new problems. The heart is extremely sensitive to a laser pulse at certain times during its cycle. A laser pulse striking the heart at the T time of the ECG wave, for example, could cause the heart to fibrillate and result in heart failure. If the heart is stopped during the procedure this problem can be avoided. But stopping the heart requires cooling the heart and connecting the patient to a heart-lung machine with all the attendant increased risks that this brings including prolonged recovery times. A beating heart, on the other hand, is difficult to administer this technique to because as the heart contracts and expands the surface may not remain normal to the laser beam, the heart wall changes distance from the focus of the beam, and the thickness of the wall changes so that the positioning of the laser handpiece and the power of the beam required are varying and unpredictable. This makes precise location of laser beam on the heart difficult so that not only will the holes not be properly located, but other areas of the heart which should not be struck may well be struck. Further, when the technique requires stopping the heart the chest must be cut open including cutting the sternum, which is especially risky because the sternum is a primary source of red blood cells.